An orthogonal frequency division multiplexing (OFDM) method is used in wireless communication systems including an IEEE 802.11 wireless local area network (WLAN) and an IEEE 802.16 wireless metropolitan area network (MAN), and in digital broadcasting systems including a digital multimedia broadcasting (DMB) system. In this case, a fast Fourier transform (FFT) processor is one of the most important constituent elements in the OFDM system.
An FFT algorithm is used to operate a discrete Fourier transform operation at a high speed, and the discrete Fourier transform (DFT) operation is given as Equation 1.
                                                        X              ⁡                              (                k                )                                      =                                          ∑                                  n                  =                  0                                                  N                  -                  1                                            ⁢                                                x                  ⁡                                      (                    n                    )                                                  ·                                  W                  N                  nk                                                              ,                      k            =            0                    ,          1          ,          2          ,          …          ⁢                                          ,                      N            -            1                          ⁢                                  ⁢                  where          ,                                          ⁢                                    W              N                        =                          ⅇ                                                -                  j                                ⁢                                                      2                    ⁢                    π                                    N                                                              ,                      N            =                          2              r                                                          [                  Equation          ⁢                                          ⁢          1                ]            
Here, X(K) denotes a result of the Fourier transform, x(n) denotes a FFT input data row, and WN denotes a twiddle factor, which are formed as complex numbers. In this case, the twiddle factor is a periodic function used to convert a time domain signal to a frequency domain signal. The FFT algorithm is performed to realize Equation 1.
Various methods for realizing the FFT algorithm have been suggested, which include a Radix-2 method and a Radix-4 method. Here, a configuration and a controlling operation of the Radix-4 method is more complicated compared to that of the Radix-2, but the Raix-4 method is more widely used since it has better multiplication performance. In the Radix-4 FFT algorithm, complex multiplication of the twiddle factor is performed, and twiddle factor values are stored in a memory.
An algorithm by M. Hasan and T. Arslan has been suggested to reduce the memory area of the twiddle factors in the FFT processor. In the algorithm, since all twiddle factors are formed in blocks by using a symmetry characteristic of the twiddle factor in the Radix-2 FFT processor,
  N  2twiddle factors are reduced to
      N    8    +  1twiddle factors.
However, the above algorithm is used in the Radix-2 method. In addition, it is required to respectively apply different memory address calculations and output equations for the respective divided blocks. That is, a memory address calculation and a realizing configuration that are commonly applied to the respective blocks are not suggested.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.